Forgeable alloy for hightemperature use



Patented July 8, 1947 ronoaanm ALLOY FOR mon- TEMPERATURE USE Rudolf H.Tliielemann, Schenectady, N. -Y., assignor to General Electric Company,a corporation of New York No Drawing. Application March 1, 1941, SerialNo. 381,377

The present invention relates to alloys, and more particularly to alloyswhich are readily forgeable, which have high creep and rupture strengthsat elevated temperatures and are suitable for use at temperatures up toabout 1400 F.

In the design and manufacture of certain types of high temperatureequipment, it is desirable to employ alloys which have good hightemperature properties and at the same time are readily forgeable andmachinable. Commercially available alloys which can be worked in thismanner are not strong enough to meet the high temperature requirements.On the other hand, commercial alloys which have high strength at thetemperatures involved either cannot be forged readily, as in dropforging operations, or they do not have the necessary oxidation andcorrosion resistance.

It is an object of the present invention to provide an alloy which isreadily forgeable in large sections and easily machinable which resistsscaling when subjected to exhaust gases from airplane engines and thelike, which maintains its metallurgical stability at operatingtemperatures up to 1400 F., and which has high long time load carryingability at temperatures up to but not materially in excess of 1400 F.

A further object of the invention is to provide an alloy which isparticularly desirable for use as forged parts in both gas andsupercharger turbines. v In a gas turbine such parts include wheels,rotors, brackets, nozzles and valves. In supercharger turbines, theparticular application for the present alloy is the turbine wheel. Such8 Claims. (Cl. 75-128) wheels generally are forged in a contour forgingdie, and therefore require a material which has exceptional hightemperature properties ancl with good forgeability and machinability hasthe following composition:

- Per cent Carbon 0.30 to 0.50 Manganese 0.40 to 0.60 Silicon 0.40 to0.60 Chromium 14 to 16 Nickel 24 to 26 Molybdenum 4 to 6 Columblum 1.5to 2.5

Remainder, iron.

My improved alloy can be made in either an are or induction type furnacein accordance with well known metallurgical practice. Large ingots canbe forged and rolled by employing the same technique required forworking chromium-nickel austenitic type alloys. The present alloy can bewelded by either the electric are or atomic hydrogen processes.

To obtain the best high temperature properties the alloy is heattreated, the heat treatment varying somewhat with the particularapplication. Generally the alloy is precipitation hardened by heating atabout 1050" C. to 1250 C. preferably about 1200 C. for about two hours,quenching in oil or water and then drawing at about 600 to 800 C.preferably about 700 C. for about two hours after which it may be aircooled. The

drawing temperature employed will depend some- ,what upon the propertiesrequired in the alloy. The alloy, heat treated in this manner willmaintain its metallurgical stability up to a temperature of about 1400F.

If desired bar stock may be heated to forging temperature, for exampleabout 1150 C., and forged to within about 10% of the required finishedsize. The partly forged alloy is then heated at about 1050 to 1250 C.for about two hours and quenched in oil or water. The alloy is thenheated to a temperature of about 650 C. forged to the desired finishedsize andthereaf-ter given a draw at about 650 to 850 C. preferably forabout two hours. The cold working from 650 C. results in a morecomplete'precipitation hardening reaction and improved properties in thealloy.

As hereinbefore set forth, the alloy may be forged readily and when dropforged or upset it has high resistance to cracking and bursting.

commercial 3 For an alloy of this type it is readily machinable and hasexcellent resistance to oxidation and scaling at temperatures up to 1800F. In the form of iorged turbine wheels, the alloy, after heat treatinghas a short time tensile strength at 1500 F. of about 55,000 pounds persquare inch. In the form of small drop forged turbine buckets which havebeen cold finished and heat treated, both as hereinbefore set forth-theshort time tensile strength at 1500 F. is about 65,000 pounds per squareinch.

The long time rupture properties of the alloy at 1200 F. and 1300 F. inthe quenched and drawn condition are as follows:

M At 1300 F Time for Time for Stress stress -lsq. iii. iflgf ib./sq i,tig s e,

The stress for 1% of creep after a given period of time can becalculated approximately by dividing the corresponding rupture stress byabout 1.5.

Small gas turbine wheels operate at speeds up to 30,000 revolutions perminute. The tempera- 1 is particularly suitable for use as such wheelsnot only because of its excellent high temperature properties butbecause its cost is not excessive and it has excellent working as wellas high temperature properties. Prior to the present invention theseturbine wheels generally have been machined out of relatively largepancake blocks of material. However, since the present alloy is readilyforgeable in contour dies it is possible to effect a saving of materialand time in the fabrication of such wheels.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A forgeable alloy containing about 0.30% to 0.60% carbon, about 0.30%to 1.50% manganese, about 0.40% to 0.60% silicon, about 12% to 18%chromium, about 20% to 40% nickel, about 2% to 8% molybdenum, about 1%to columbium with the remainder substantially all iron.

2. A forgeable alloy containing about 0.30% to 0.50% carbon, 0.40% to0.60% manganese, 0.4% to 0.60% silicon, about 14%,to 16% chromium, about24% to 26% nickel, about 5% of molybdenum, about 2% columbium'with theremainder substantially all iron.

3. A forgeable alloy which is characterized by good oxidation resistanceat temperatures up to 1800 F. by its metallurgical stability at temperatures up to 1400 F. and by its high rupture strength and resistance tocreep at temperatures about 1000 F., said alloy containing a pluralityof ingredients of which the following in the proportions stated are theonly ones necessary to attain said characteristics:

Per cent Carbon .30 to .60 Chromium "1..---- 12to 18 Nickel 20 to 40Molybdenum 2to 8 columbium lto 5 Remainder, substantially all iron.

4. A forgeable precipitation hardened alloy containing about 0.30% to0.60% carbon, about 0.30% to 1.50% manganese, about 0.40% to 0.50%silicon, about 12% to 18% chromium, about 20% to 40% nickel, about 2% to8% molybdenum, about 1% to 5% columbium with the remainder substantiallyall iron.

5. A forgeable precipitation hardened alloy containing about 0.30% to0.60% carbon, 0.40% to 0.60% manganese, 0.40% to 0.60% silicon, about14% to 16% chromium, about 24% to 26% nickel, about 5% of molybdenum,about 2% columbium with the remainder substantially all iron.

6. The method of hardening an alloy containing about .30% to .60%carbon, about .50% to .80% manganese, about .40% to .60% silicon, about12% to 18% chromium, 20% to 40% nickel, 2% to 8% molybdenum, 1% to 5%columbium with the remainder substantially all iron, which comprisesheating the alloy for about two hours at a temperature of 1050" to 1250C., quenching the alloy and then drawing it at a temperature of about650 to 750 C. for about two hours.

7. The method for improving the properties of an alloy containing about.30 to .60% carbon, about .30 to 1.50% manganese, about .40 to .60%silicon, about 12 to 18% chromium, about 20 to 40% nickel, about 2 to 8%molybdenum, about 1 to 5% columbium with the remainder substantially alliron which comprises heating the alloy to a' forging temperature,forging the alloy to within about 10% of the desired finished siz'e,

' heating the alloy to a temperature sufllcient to produce a conditionof solution in the alloy,

quenching the alloy, cold working it to finished REFERENCES CITED Thefollowing references are of record in the file of this patent:

FOREIGN PATENTS Number Country Date 374,541 Great Britain June 16, 1932375,777 Great Britain June 30,1932

OTHER REFERENCES U. S; S. Carilloy Steels, page 199, published in 1938.

